A human microbiome is considered to be the aggregate of microorganisms that reside on the surface and in deep layers of the skin, in the saliva and oral mucosa, in the conjunctive, an in the gastrointestinal tracts. A human microbiome is thought to be composed of at least ten times as many bacterial cells as human cells, and these bacterial communities are known to have major impacts on the systems in which they reside. For example, recent studies have implicated the human microbiome in many human diseases.